The investigator plans to use line bisection as an index of biases in spatial attention in normal subjects presumably resulting from some kind of hemispheric competition. In particular he proposes to measure line bisection as a function of line length and line position, and use this data to infer spatial attentional distribution across the right and left hemispheres as postulated in a model by Anderson. In addition, he plans to vary line contrast to see if these distributions are purely attentional or reflect stimulus salience more generally